Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$29.83	3.632%	$30.9134	$30.91	$30.90	$30.90
Purchase #2	$17.64	6.408%	$18.7704	$18.77	$18.75	$18.80
Purchase #3	$186.59	3.437%	$193.0031	$193.00	$193.00	$193.00
Purchase #4	$83.70	7.168%	$89.6996	$89.70	$89.70	$89.70
Purchase #5	$221.35	8.568%	$240.3153	$240.32	$240.30	$240.30
Purchase #6	$80.37	11.634%	$89.7202	$89.72	$89.70	$89.70
Purchase #7	$39.79	8.169%	$43.0404	$43.04	$43.05	$43.00
7 purchase totals =	$659.27		$705.4624	$705.46	$705.40	$705.40